This invention concerns apparatus and a method of making a commutator for relatively small electric motors, the segments of which are separately inserted into a mold intermediary plate during manufacture, filled with a plastic material, preferably a thermosetting plastic material.
Usually commutators consist of a cylindric body of plastic material to the circumference of which several segments are imbedded. In the finished form, such a commutator must have its segments (bars) separated from each other by slots which are not filled with the plastic body material. Otherwise, the plastic material normally used wears in the course of time and projecting plastic webs are formed between adjacent segments. This results in accelerated wear of the carbon brushes and in the generation of increased noise. Still more disadvantageous is the fact that such projecting plastic webs can produce brush contact dead spots to that if the motor is stopped in such a position in which a carbon brush springs back over these plastic webs, no brush contact is extant and the motor will not start. Thus, the formation of such plastic webs is detrimental to motor reliability and life. In the production of the individual segments in practice, tolerances as tight as .+-.0.02 mm between adjacent segments may be required. Even with such tight tolerances, thin plastic films can be created between the edges of individual adjacent segments and these films can have disadvantageous effects as described. Until now, manual removal of the films was required, preventing the automation of the process and consequent minimization of manufacturing costs. The manner in which the present invention provides an improved process ad structure for commutator manufacture will be evident as this description proceeds.